Commercially, sulfonic acid is reacted with lime, methanol, xylene, carbon dioxide, and calcium hydroxide to produce a high BN overbased alkylaryl sulfonate. The high BN sulfonate is often passed through a centrifuge to remove sediment. For every 10,000 metric tons of sulfonate final product produced, there is about 900 metric tons of sludge residue. That sludge residue (a cake) comprises about 20% lime and calcium carbonate, about 20 to 25% high BN overbased alkylaryl sulfonate with calcium carbonate dissolved in the sulfonate, and about 55% solvent (e.g., xylene). For the time being, this sludge residue is burned, which is not desirable economically or environmentally.
A similar problem results, to some extent, in the production of a commercial overbased sulfurized alkylphenate, which produces a similar sludge residue that is normally burnt. In a typical commercial process, an alkylphenol is reacted with sulfur, lime, and glycol, preferably associated with a mono alcohol, in the presence of a low overbased sulfonate and diluent oil, then the product is overbased with carbon dioxide. The production of such an overbased sulfurized alkylphenate is described in British patent 1,015,769.